Metrohm NIRS XDS RapidContent, Manual, Page: 48 / 50

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Glossary
AU
Absorbance Units ; unit of the (actually dimensionless) absorbance.
Data interval
Distance of nearby data points on the wavelength axis; depends on the
angle between nearby grid positions. Not to be confused with the optical
bandwidth; the spectral data interval does not show the optical resolution
of the spectrometer.
Optical bandwidth
The optical bandwidth is the spectral broadening of an ideal monochro-
matic light source with a spectrometer. It is determined by the spectral dis-
persion of the monochromator, among other things.
Optical pathlength
Distance a light beam covers in a sample from entry point to exit point. In
transmission measurements of clear samples, the optical pathlength is the
same as the thickness of the sample, in reflection measurements it
depends on different factors (particle size, packing density, and others).
Photometric noise
Statistical fluctuations of the measured absorbance.
Reflection measurement
Reflection measurements are performed on diffuse scattering or opaque
materials. Hereby the light that is remitted out of the sample by the scat-
tering angle is detected.
Transflection measurement
Transflection measurements enable the measurement of absorption spec-
tra of transparent samples in reflection geometry. Hereby the light going
through the sample is reflected with a mirror in the direction of the
incoming light beam and collected, for example with a fiber.
Transmission measurement
Transmission measurements are performed on transparent samples.
Hereby the light that directly goes through the sample (along the optical
axis) is detected.
Wavelength accuracy
Absolute deviation of measured and actual wavelength.